Research proposed involves investigation of genetic variation in animals' requirements and metabolism of nutrients, to determine the degree of genetic variation in requirements for certain nutrients, to given an indication as to the feasibility of making changes in food requirements of animals through genetic selection. Through genetic selection, interrelationships of certain nutrients can be studied more effectively because of the selective populations of animals used. Research will deal principally with genetic variation in lysine and arginine metabolism and variation in the conversion of tryptophan to nicotinic acid. Strains of chickens will be maintained which differ markedly in requirement for arginine, dietary lysine, and nicotinic acid. These strains will be further differentiated by selection. Proposed arginine metabolism studies involve factors affecting levels of the enzyme arginase in chick kidney and the regulation of levels of enzyme in chick kidney primarily by the body pools of lysine. Genetic variation in lysine metabolism of chickens selected for high or low requirement for arginine will be investigated, particularly the variation in the enzyme lysine-alpha-ketoglutarate reductase. Strains differing in dietary nicotinic acid requirement, the conversion of tryptophan to nicotinic acid, will also be investigated.